The competition to sell disk drives at ever lower prices is intense. Manufacturers of disk drives are constantly developing new ways to cut the costs of manufacturing disk drives in order to sell their disk drives at competitive prices and to stay in business. FIG. 1 depicts a block diagram of a disk drive. Typically, data is read from and written to the recording disk 110 of a disk drive in circular tracks. Circular track positioning information 130 (CTPI) is typically written permanently to recording disks, such as recording disk 110, for example at the manufacturers, to facilitate reading data from and writing data to the recording disks 110. The CTPI 130 can include a pattern of radial positioning information A1, B1, A2. The radial positioning information A1, B1, A2 are commonly referred to as “servo bursts” and the pattern of the radial positioning information A1, B1, A2 is commonly referred to as a “servo pattern.” The CTPI 130 is used during operation of the disk drive to ensure that the head of the disk drive is centered over the desired track of data 160, 170. For example, the CTPI 130 is used to determine where to write data to and where to read data from.
Typically a complete CTPI 130 includes radial positioning information A1, B1, A2 that are written on the recording disk 110 from the outer diameter 140 (OD) to the inner diameter 150 (ID). Although FIG. 1 depicts only a part of a CTPI 130, for the sake of simplification, the discussion herein shall refer to the CTPI 130 as if it were a complete CTPI 130.
The CTPI 130 is written to a recording disk 110 using a writing mechanism. For example, as the recording disk 110 spins around, the writing mechanism writes the CTPI 130 to the recording disk 110. The writing mechanism can include the write head of the disk drive, the suspension arm that the write head is attached to and what is commonly known as a “pusher” that mechanically pushes the suspension arm. The “pusher” mechanically pushes the suspension arm to position the write head to a desired location of the recording disk 110. In contrast the writing mechanism may not use a pusher. For example in this later case, the writing mechanism can include software that controls the suspension arm to position the write head over the desired location. The software programs can be executed on a general purpose computer or a special purpose microcontroller, among other things.
To avoid errors while reading or writing data, it is desirable that each track of data 160, 170 be as close to a perfect circle that is centered on the recording disk 110 as possible. Since the disk drive uses the CTPI 130 to determine where to write data to and/or to read data from, the placement of the CTPI 130 on the recording disk 110 directly affects the placement of the tracks of data 160, 170 on the recording disk 110.
FIG. 1 depicts ideal tracks of data 160, 170 that are perfect circles that are centered around the recording disk. However, in reality due to various factors that will be discussed, tracks of data 160, 170 are not perfect circles as is the case in the real world. In contrast, FIG. 2 is a block diagram of a disk drive depicting tracks of data 210, 220 that deviate from perfect circles. As the recording disk 110 spins, the air around the writing mechanism exerts force against the writing mechanism causing it to vibrate and causing the CTPI 130 to deviate more and more from a perfect circle. The faster the recording disk 110 spins, the greater the force that the air exerts on the writing mechanism and the more the CTPI 130 deviates from a perfect circle.
Deviation of a track of data 210, 220 from a perfect circle or off center 180 can cause a track of data 210, 220 to come close to an adjacent track of data 210, 220 resulting in a loss of data during a write process. For example, assume that tracks of data 210 and 220 are adjacent to each other on the recording disk 110 and data has already been written to track of data 210. At a particular point, while writing data to track of data 220, the data on track of data 210 may be overwrite when the data for track 220 is written at a particular point, referred to as a “squeeze point 230,” where the two adjacent tracks of data 210, 220 are close together.
One method of reducing the imperfections of the CTPI 130 involves reducing the speed at which the recording disk 110 spins as the CTPI 130 is written to the recording disk 110. Typically, the CTPI 130 is written at half the speed that a disk drive is capable of spinning its recording disk 110. However, this greatly increases the length of time it takes to write the CTPI 130 to recording disks 110, thus, increasing the cost of manufacturing disk drives. A disk drive can spin as fast as the design of the disk drive allows it to spin at. This speed shall be referred to hereinafter as “Design revolutions per minute (RPM).”
For these and other reasons, a method that reduces the imperfections when writing circular track positioning information to a recording disk would be valuable.